(1) Field of the Invention
The present invention relates generally to control systems for suspended objects and more specifically to a control system and method for stabilizing a single line suspended mass in yaw.
(2) Description of the Prior Art
Transporting objects suspended in air can be a difficult task, particularly when dealing with extreme weather conditions and harsh environments. These outside disturbances can greatly increase the risk of injury to those people charged with controlling the suspended objects, as well as bystanders in proximity to the suspended object. Furthermore, the load being moved is susceptible to damage as the outside forces alter the roll, pitch, and yaw of the suspended object.
Multiple cables may be utilized to lift loads and control spinning or yaw. However, controlling multiple lift cables adds greatly to system cost, complexity and maintenance, while reducing the maneuverability of the lifting mechanism. Further, the angular position of the load in this case is typically not readily adjustable and often must remain in a single orientation.
Torque balanced cables may be used to control yaw but are not resistant to disturbances from weather impacts or other outside forces. In extreme environments, a torque balanced cable will do little to resist changing yaw.
The problems discussed above are well known in the construction industry in dealing with transporting supplies from the ground to a point high above ground, e.g., a skyscraper, oil rig, and the like.
When dealing with operations at sea, such as Navy shipboard exercises, or private rescue operations for people and/or vessels, a wave slap event or excessive wind can cause the suspended mass to rotate multiple revolutions which in turn may cause severe damage to the fairings and, in extreme cases, the cables may be damaged beyond use.
U.S. Pat. No. 8,226,042 to Howell et al., issued Jul. 24, 2012, which is incorporated herein by reference, describes a spin control system that includes first and second thrusters coupled to an object hanging from a suspension member. When activated, the first and second thrusters generate thrust in opposing directions that are substantially perpendicular to the longitudinal axis of the suspension member. When the object spins, a controller activates at least one of the first and second thrusters to approximately align the object with a reference position.
While U.S. Pat. No. 8,226,042 teaches the basic equipment that could be utilized in a spin control system, the patent does not describe a control system that is effective in using the thrusters for controlling spin or yaw. The patent requires unspecified reference information or manual inputs that can be used to predict the spin rotation, which then determine which thruster to operate. The patent also assumes that the suspended equipment remains in a particular reference position that does not vary in pitch or roll, which can affect the working distance between the thruster and cable and the resulting amount of foot pounds of force produced by the thrusters. Moreover, the patent does not provide the factors involved in making a prediction of the anticipated direction of spin or method for responding without a prediction of anticipated direction of spin. Also, the patent does not teach any means to counteract environmental factors, cable spring and damping factors that affect spin and pitch changes, or system noise from the thrusters, winches, helicopter or other system noise that affects the ability of the control system to operate effectively for this purpose.
Accordingly, a need exists for an improved spin or yaw stabilization control system that can more effectively counter undesired rotation of a single cable suspended mass in yaw. Accordingly, those of skill in the art will appreciate the present invention which addresses the above discussed issues.